Replacement for crit: Special Strike.
As a league player I don't like the RNG aspect of Crit, but when I was playing Blitz I trolled and bought IE and saw blitz crit animations for the first time and it was AWESOME. Deal is that the animator have made a crit animation for every character so I feel like those animations should be seen more in 0 cs sups. From playing Dynasty and Samurai Warriors I've come up with a compromise that works slightly like the Musuo gauge.
Special Attack: *Every auto attack, cdr%, movement, abilty cast, and damage recieved by enemy champion sources builds your special attack gauge when it reaches 100 you deal bonus damage. Essentially anything you do on the rift builds your damage.
Ok so here's how we can replace crit with a reliable stat that can be managed and balanced and have it apply to all characters. Crit items now are replaced by special attack regen bonus items (gives bonus % gains to the special attack gauge) and certain Item's deal procs based on special attacks. This could open the way for more hybrid items. Each new Special Attack item will have a toggle and only 1 can be active at a time. This way a champ (Ezreal) doesnt slow, deal bonus damage, bonus lightning aoe, and other procs all at once. This will make champs have to chose what would be better in a fight (single damage, restore, aoe, cc)
IE will deal 250% bonus special attack damage. Statick Shiv will deal a special attack that hits 4 targets, PD will deal a special strike where you double strike (the double strike counts towards your next special attack), Sheen items have a special attack that deals bonus ad(for sheen IG and TF) and bonus md(for LB) and restores 10 mana and increases ms by 30 for Trinity slows champions with IG. Ravenous Hydra deals aoe daamge that heals
This is just a basic idea though essentially they could change lots of their items to have special attack toggles.